Cables used for transmission of data or electricity and pipelines used in transporting liquids, gases and other fluid media are mostly buried underneath the soil, and are therefore subject to corrosion. To prevent the possibility of accidents due to spillage of the media being transported, the cables and pipelines are usually coated with an insulating barrier that separates them from the corrosive effects of the soil. However, over time, these insulating coatings wear out and certain portions of the cable or pipeline become exposed to the soil. The exposed parts of the cables or pipelines, where direct contact with the surrounding soil is established, are called “anomalies” or “holidays”.
Several methods of pipeline integrity and corrosion mitigation are currently available for monitoring the state of the buried pipelines. They include close interval potential survey (CIPS), direct current voltage gradient (DCVG), alternating current voltage gradient (ACVG), and alternating current—current attenuation (ACCA). The use of these methods for the indirect assessment of the state of the underground structure functions is done primarily by determining the change in certain parameters along the length of the structure. When these parameters exceed certain magnitudes, the presence of a coating holiday, or coating anomaly, is suspect.